A combination is a grouping of a set of items for which the order does not matter. For example, ABC would be considered the same combination as BAC or CAB. When the order does matter, it’s called a permutation. When calculating a possible number of combinations, we can use the formula for nCr, where n represents the total number of items to be chosen from, and r represents the number of items we are choosing (“n” different things chosen “r” at a time”):